Forest fires, brush fires,
and slash and burn agriculturetypes of biomass burningare a significant
force for environmental change, both locally and globally. Intentional
deforestation by burning radically alters local landscapes. At regional scales,
fires naturally shape ecosystems such as the boreal forest (Canada, Alaska, and Russia) and
chapparral (Southern California). Globally, fires may play an important role in climate change,
emitting both greenhouse gases and smoke particles (aerosols) into the atmosphere.
These emissions almost certainly played a role in the 0.5° Celsius increase in the
Earth's average surface temperature over the past 100 years.

Current global estimates of gas and particulate (aerosol) emissions from biomass burning
in the open literature are extremely approximate and vary considerably:

These
emission products promote the formation of polluted clouds
and affect the Earth's radiant energy budget (heat and sunlight) in
ways that influence climate on a regional and global scale.

Fire has always been and continues to be an integral part of land use and
culture around the World. Earth Scientists are placing greater emphasis on
obtaining more accurate assessments of emissions from biomass burning. Remote
sensing of fires, smoke and even burn scars (transformed area where the fire
burned) allows for improved detection of fire characteristics as well as their
short- and long-term effects on ecosystems.

Top Left: Fires occur frequently in most forest ecosystems, which are adapted
to regular wildfire outbreaks. (Photograph courtesy Canadian Fire Research)

Why are Fires Important?

Fires
play an important role in the natural changes that occur in Earth's
ecosystems. The diversity of plant and animal life in the world's
forests, prairies, and wetlands is (partly) dependent on the effects of
fire; in fact, some plants cannot reproduce without fire (fire breaks
open the outside coating of some seeds and stimulates germination). What
may at first look like total devastation soon becomes a panorama of new
life. Fire initiates critical natural processes by breaking down organic
matter into soil nutrients. Rain then moves these nutrients back into
the soil providing a rejuvenated fertile seedbed for plants. With less
competition and more sunlight, seedlings grow more quickly.

Wild animals deal with fire remarkably well. Birds fly out of the
fire area, large animals leave the danger zone by escaping to ponds and
streams, while others return to their burrows. Usually few animals are
killed by fire.

Prescribed fire is one of the most important tools used today to
manage Earth's diverse ecosystems. A scientific prescription, prescribed
fires help create a mosaic of diverse habitats for plants and animals.
If all fire is suppressed, fuel (grasses, needles, leaves, brush, and
fallen trees) can build up and allow larger, and sometimes
uncontrollable, fires to occur. If enough fuel builds up, the fires could
be so intense that they may destroy the seeds in the soil and hinder new
tree and plant growth. By burning away accumulated fuels, planned fires
make landscapes safer for future natural fires.

State of the ScienceBy 1990, global tropical deforestation was occurring at a
rate of about 1.8 percent of the world's total forest lands per year.
Approximately 142,000 square kilometers of rainforest are eliminated
annuallyan area slightly larger than the state of Arkansas (more information on this topic can
be found in the Tropical Deforestation Fact Sheet). Using data
from satellite sensors, aircraft, and ground-based initiatives,
scientists are working to develop a new global fire monitoring program
that will enable them to better understand the myriad implications of
this growing problem. Specifically, efforts are underway to quantify the
total area of forests and grass land burned each year and to more
precisely estimate the amount of resulting emission products. These
newer and better data will facilitate development of more robust
computer models that will enhance scientists' abilities to predict how
biomass burning will impact climate, the environment, and air quality.

Top Left: Burned vegetation quickly releases nutrients back into the soil,
nurturing the rapid growth of new vegetation. These jack pine seedlings germinated after
a fire softened pinecones littering the forest floor, releasing the seeds they held.
(Photograph courtesy Forrest Hall, NASA GSFC/University of Maryland)

Trace Gas Emissions

Since the beginning of the industrial revolution, humans have
transformed about 40 percent of Earth's land surface and have increased
carbon dioxide levels by about 25 percent. Scientists estimate that from
1850 to 1980, between 90 and 120 billion metric tons (90-120 trillion
kilograms) of carbon dioxide were released into the atmosphere from
tropical forest fires. Comparatively, during that same time period, an
estimated 165 billion metric tons of carbon dioxide were added to the
atmosphere by industrial nations through the burning of coal, oil, and
gas. Today, an estimated 5.6 gigatons of carbon are released into the
atmosphere each year due to fossil fuel burning. Burning of tropical
forests contributes another 2.4 gigatons of carbon per year; or, about
30 percent of the total.

Over the last decade, it seems that the regional distribution of biomass
burning has increased worldwide, as well as the length of burning time.
The result is a continuing increase in the release of emission products,
and an increase in the severity of their impact on climate and on the
environment. Scientists estimate that in just a few months the burning that
took place in 1997 in Indonesia released as many greenhouse gases as all
the cars and power plants in Europe emit in an entire year.

After carbon dioxide, the most significant greenhouse gas is methane,
another emission product from biomass burning (about 10 percent
globally). Although methane is about 200 times less abundant than carbon
dioxide in the atmosphere, molecule for molecule methane is 20 times
more effective at trapping heat. Since the beginning of the Industrial
Revolution, methane has doubled in the troposphere. Additionally, its
concentration has been increasing about 1 percent per year, so
scientists are concerned that its relative significance as a greenhouse
gas may dramatically increase in the future, although there are
indications that this increase may have slowed down in the last decade.

Nitrous oxide (N2O) concentrations have been increasing at about 0.3
percent per year for the last several decades. Yet, nitrous oxide has a
lifetime of 150 years in the atmosphere, which contrasts sharply with
the 10-year lifetime of methane. A single nitrous oxide molecule is the
equivalent of 206 carbon dioxide molecules in terms of its greenhouse
gas effect. Biomass burning accounts for about 2-3 percent of the total
amount of tropospheric nitrous oxide. Emissions of nitrous oxides and
methane are further associated with the production of tropospheric
ozone. Unlike "good" ozone in the stratosphere (upper atmosphere) that
acts as a shield to screen out the sun's harmful ultraviolet rays, ozone
in the troposphere is a pollutant that, when breathed, damages lung
tissue and is also harmful to plants.

Greenhouse gasessuch as carbon dioxide, methane, and nitrous oxideare
mostly "transparent" to incoming solar radiation; that is, they rarely
interact with sunlight. However, these gases are very efficient at trapping heat
radiated from the Earth's surface by absorbing and re-emitting it.

There is a wide margin of error in the estimates of biomass burning given abovesignificantly more
error than in our estimates of industrial emissions. The accuracy of
scientist's biomass burning emission estimates must be improved if they
are to better understand, model and predict the impacts of the emissions
on climate change.

Top Left: In addition to the visible plume of smoke and ash, fires release gases such as
carbon dioxided and methane into the atmosphere. The gasses from wildland fires may
play an important part in future global climate change. (Photograph courtesy Yoram Kaufman,
NASA Goddard Space Flight Center)

Aerosol Emissions

Smoke and aerosol particles from large-scale biomass burning can rise
high into the troposphere and be carried long distances by wind
currents. Smoke plumes from Mexico have traveled as far north as
Wisconsin and the Dakotas, and as far east as Florida and out over the
Gulf Stream.

Aerosols
have a two-fold cooling effect on climate. In the open
atmosphere, they scatter and absorb incoming solar radiation, thereby
reducing the amount of sunlight that reaches the surface. Moreover,
aerosols act as "seeds"called cloud condensation nuclei. When clouds
form in the polluted atmosphere, the clouds' droplets tend to be smaller
and more numerous. Because polluted clouds are typically comprised of
more densely-packed droplets, they are more efficient at absorbing and
reflecting sunlight, again having a cooling effect on the surface.

Aerosols represent one of the greatest areas of uncertainty regarding
climate change, both on global and regional scales. Scientists do not
fully understand the magnitude of their cooling influence on climate.

Scientists do not know which of the emission products exerts the greater
net effect on regional and global climatethe cooling influence of
aerosols and clouds, or the warming influence of the greenhouse gases.
Because both types of emission products change rapidly through time and
space, they are difficult to observe and characterize. In the future,
the greenhouse gas warming is expected to dominate due to the gases'
much longer presence in the atmosphere (10-100 years) than that of
aerosol particles (7 days).

Above Left: Smoke from fires in
Guatemala and Mexico on May 14, 1998, drifted across the Gulf of Mexico and triggered air
quality warnings along the U.S. Gulf Coast. In addition to human health concerns, smoke
particles affect rainfall rates and global climate. (Image by Norman Kuring,
NASA SeaWiFS Project)

NASA and NOAA Missions for Monitoring Global Fires

Different satellites provide observation and measurement capabilities
for monitoring different fire characteristics: areas that are dry and
susceptible to wildfire outbreak, actively flaming and smoldering fires,
burned area, and smoke and trace gas emissions. Several satellite
systems are currently available for fire monitoring with different
capabilities in terms of spatial resolution, sensitivity, spectral
bands, and times and frequencies of overpasses.

Fires vary widely in size, duration, temperature, and in the tropics,
where it is moist and humid, fires have a strong diurnal cycle. No one
system provides optimal characteristics for fire
monitoringmulti-sensor data fusion is needed to optimize the use
of current systems.

Flown on
NOAA Polar Orbiting Environmental Satellites, the Advanced Very
High Resolution Radiometer (AVHRR) measures electromagnetic radiation
(light reflected and heat emitted) from our planet. AVHRR was originally
intended only as a meteorological satellite system but it does have
applications for fire monitoring. AVHRR remotely senses cloud cover and
sea surface temperature, enabling its visible and infrared detectors to
observe trends in vegetation, clouds, shorelines, lakes, snow and ice.
The visible bands can detect smoke plumes from fires as well as burn
scars. The thermal infrared band can detect actual hotspots and active
fires. Its ability to detect fires is greater at night, since the
system can confuse active fires with heated ground surfaces, such as beach
sand and asphalt.

Active fire
mapping on a global scale using a single satellite system has been coordinated by the
International Geosphere Biosphere Program (IGBP) using AVHRR data for 1992-93 from international
ground stations.

In addition, a small number of
countries have developed their own regional AVHRR satellite fire
monitoring systems using direct read-out; e.g., Brazil, Russia, and
Senegal. Research groups have provided regional examples of trace gas
and particulate emissions from fires for Brazil, Southern Africa,
Alaska.

The
Geostationary Operational Environmental Satellites (GOES) house a
five-channel (one visible, four infrared) imaging radiometer designed to sense
radiant and solar reflected energy from sample areas of the Earth. They are
stationed in orbits that remain fixed over one spot on the equator, providing
continuous coverage of one hemisphere. GOES satellites aquire images every
1530 minutes, at up to 1km resolution in visible light, for the detection
of smoke, and 4km resolution in thermal infrared to directly detect the heat of
fires.

The Landsat
series of Earth-observing satellites monitor characteristics
and changes on the surface of the Earth at high resolution (up to 15m
per pixel). The original missions (1970s 
early 1980s) used the Multispectral Scanner (MSS) which was only
capable of detecting scars. Current Landsat series satellites use the
Thematic Mapper (TM) and Enhanced Thematic Mapper Plus (ETM+) to provide land surface information.
The seven bands (eight on Landsat 7's ETM+) monitor different types of Earth resources over a wide
area (81 North and 81 South Latitude). The thermal band enables the
system to detect "hotspots." Landsat 7 provides impressive high-resolution
images but only infrequently, revisiting an area every 14 days.

The
Total Ozone Mapping Spectrometer (TOMS) is a measuring device that
provides data regarding ozone levels. Measured in Dobson Units (DU),
TOMS produces a complete data set of daily ozone levels around the
world. This instrument is the first to show aerosols (airborne dust and
smoke particles) over land. It also provides the ability to distinguish aerosols
that absorb light from aerosols that reflect it. TOMS makes 35 measurements every 8
seconds, each covering 50-200 kilometers wide on the ground. Close to
200,000 daily measurements cover almost every spot on the Earth except
for areas near the poles. These data make it possible to observe a variety
of Earth events including forest fires, dust storms and biomass burning.

The
Tropical Rainfall Measuring Mission (TRMM) carries a high-resolution
sensor similar to AVHRR, called the Visible and Infrared Scanner (VIRS),
which is capable of spotting active fires as well as evidence of burn scars.
It has five bands from visible to thermal infrared (.6312µm) and
provides 2km resolution. TRMM's primary purpose is to measure rainfall
over both land and oceans from 30° South to 30° North
Latitude. TRMM is unique in that previous satellites tended to show the
tops of clouds whereas TRMM instrumentation allows a look into the cloud
itself. In addition to its other sensors, TRMM carries LIS, the Lightning
Imaging Sensor. LIS provides information on both cloud to cloud and cloud
to ground lightning strikes around the world. The imager is capable of locating
and detecting ninety percent of lightning strikes in the world. This
information can help identify areas that may be particularly susceptible
to wildfire outbreaks.

In late 1999, NASA launches the first in a series of new Earth remote
sensors that will bring dramatically improved capabilities for global
monitoring of fires. The Earth Observing System's flagship
spacecraftTerra (formerly named EOS AM-1)will carry a payload of five sensors that,
collectively, greatly expand scientists' capacity for near-real-time
fire monitoring, while more accurately measuring emission products. The
Terra spacecraft will fly in a near-polar orbit, crossing the equator in
the morning when cloud cover is at a minimum and its view of the surface
is least obstructed. Subsequently, in 2000, the Aqua (formerly EOS PM-1) spacecraft will launch into a
near-polar orbit crossing the equator in the afternoon, to observe the
daily variability of surface features.

From Top: This fire occured in Laguna Beach, CA, near Los Angeles,
on November 2, 1993. It was observed by the Advanced Very High Resolution Radiometer (AVHRR),
flown on NOAA's polar orbiting weather satellites, which can detect the heat from fires in thermal
infrared wavelengths, and can image smoke in visible and near infrared bands. (Image by Robert Simmon,
NASA Goddard Space Flight Center, based on NOAA data)

In May, June, and July, 1998, several fires burned out of control on the east coast of
Florida. This image is from the Geostationary Operational Environmental Satellites, GOES-8.
Like AVHRR, the instruments aboard NOAA's geostationary weather satellites detect fires and
smoke in visible, near infrared, and thermal infrared wavelengths. Because the orbits of
GOES satellites are synchronized with the Earth's rotation, they continuously view portions
of the Earth's surface. (Image by Dennis Chesters, NASA Goddard Space Flight Center,
based on NOAA data)

The pink and yellow areas in this image are the remnants of fires - burn scars. This
image was Landsat series satellites only pass over an area once every 14 days, so they are used
to map the effects of fires, rather than their occurence and progress. (For more information
about this image, see: Mapping Landcover and Fire Extent with Satellite Data.)
(Image courtesy Dave Knapp)

Particulates contained in smoke (aerosols) are difficult to measure from satellites,
but recently NASA scientists used Total Ozone Mapping Spectrometer (TOMS) data to chart
the spread of smoke from large fire outbreaks, such as those in Western Brazil
during August, 1998. (Image by NASA Goddard Space Flight Center TOMS project)

In the spring of 1998 drought conditions led to the spread of wildfires throughout
Southeast Asia. The Island of Borneo was especially hard hit. This image from TRMM's
Visible and Infrared Scanner (VIRS) shows fires (red) and smoke (mixed with clouds) from
March 1, 1998. (Image by Greg Shirah, NASA Goddard Space Flight Center Scientific
Visualization Studio)